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- Volume 2003, Issue 199, 2003
Southern African Forestry Journal - Volume 2003, Issue 199, 2003
Volume 2003, Issue 199, 2003
Source: Southern African Forestry Journal 2003, pp 1 –5 (2003)More Less
Extracted from text ... Southern African Forestry Journal - No. 199, November 2003 1 Guest Editorial Forest Biotechnology: A South African perspective INTRODUCTION While it is a pleasure to have the opportunity to present a commentary on biotechnology as it applies to South African forestry, this is a somewhat daunting task. The problem one immediately faces pertains to the word biotechnology, which has a host of different interpretations. Broadly, biotechnology might be considered as the application of living organisms to produce or modify products for particular purposes. As such, many forestry activities and especially those linked to exotic plantation forestry could be considered as ..
Killing Eucalyptus grandis cut stumps after multiple coppice rotations in the KwaZulu-Natal midlands, South Africa : scientific paperAuthor Keith M. LittleSource: Southern African Forestry Journal 2003, pp 7 –13 (2003)More Less
The repeated regeneration of <I>Eucalyptus grandis</I> through the management of coppice shoots results in large multi-stemmed stumps that are difficult to kill. To test the most effective manner in which these stumps could be killed, a trial was initiated at felling on a fourth rotation stand of <I>E. grandis</I> stumps in the KwaZulu-Natal Midlands. Triclopyr (amine salt, 360 g l<sup>-1</sup>), triclopyr (butoxy ethyl ester, 480 g l<sup>-1</sup>), imazypyr (100 g l<sup>-1</sup>), metsulfuron-methyl (600 g kg<sup>-1</sup>) and a combination of triclopyr (butoxy ethyl ester, 480 g l<sup>-1</sup>) + glyphosate (isopropylamine salt, 192 g l<sup>-1</sup>) were applied to a basal frill, the cut surface, or the foliage of coppice regrowth of <I>E. grandis</I> stumps. These treatments were compared to an untreated control where the coppice regrowth was manually cut with an axe. Irrespective of the active ingredient, the use of herbicides proved to be more effective in preventing coppice regrowth than by manual control with an axe. The application of herbicides to a basal frill killed 90 % of the stumps and required the least follow-up control.
Effects of site management operations on the nutrient capital of a eucalypt plantation system in South Africa : scientific paperAuthor Ben Du ToitSource: Southern African Forestry Journal 2003, pp 15 –25 (2003)More Less
The Karkloof Project is a case study of the effects of intensive site management operations during the interrotational period, on (a) the nutrient capital of the system, and (b) the availability of growth resources (nutrients and water) in a commercial <I>Eucalyptus grandis</I> stand in South Africa. This paper specifically focuses on the nutrient contents in various pools of the system, namely the soil, the forest floor, and the above- and below-ground biomass. The effects of nutrient removal through harvesting operations, slash management or slash burning were examined in relation to estimates of readily plant-available nutrient pools in the system. The removal of individual nutrient elements through harvesting plus slash burning was calculated for a regime of one planted crop followed by two coppice crops. In this regime, slash burning (if used) and fertilization are normally only implemented immediately before replanting. The combined losses of harvesting and burning (averaged per crop cycle) amounted to 13, 25, 11, 5 and 3% of the readily available pools for N, P, K, Ca and Mg, respectively. The system is thus well buffered against the depletion of most macronutrients over the short term. Despite this fact, the cumulative effect of nutrient removal through successive rotations could add up to substantial amounts over long periods of time. Nutrients removed from the system need to be replenished to ensure sustained productivity in perpetuity. The comparatively large percentage loss of P is small in actual quantity (<I>ca</I>. 20 kg ha<sup>-1</sup> per crop cycle) and is commonly mitigated to some degree by recommended fertilization practices. Losses of Mg are very small relative to available Mg pools. However, N, K and Ca losses are not replenished under current management regimes and management will need to deal with this to ensure long-term ecological sustainability. Strategies to ensure sustainable supplies of these nutrients are discussed.
Site and stand age effects on fertiliser responses in Pinus patula pulpwood plantations in Swaziland : scientific paperAuthor Andrew R. MorrisSource: Southern African Forestry Journal 2003, pp 27 –39 (2003)More Less
Six fertiliser trials were established in separate stands in their 4<sup>th</sup>, 7<sup>th </sup> or 12<sup>th</sup> year on both granite and gabbro derived soils in the Usutu Forest, Swaziland. All trials compared the same factorial combination of N, P and K fertilisers. Tree growth response to fertiliser was measured five years after application. The trials demonstrate that meaningful responses to fertiliser can be obtained when applied to established pulpwood stands without thinning. Both stand age at application and soil parent material were found to influence response to fertiliser. With K, positive responses were obtained in the 3 and 6 year old stands but negative responses were evident applied to 11-year-old stands. Positive responses to K were also more pronounced on gabbro derived soils. Tree growth was improved by P applied in 6- and 11-year-old stands and by N applied in 11-year-old stands. Results are discussed in relation to nutrient cycling, stand development, soil fertility and records of long-term productivity at Usutu. It is proposed that observed declines in second rotation productivity in block A of the forest are associated with gabbro-derived soils and that this decline can be corrected by fertiliser application.
Does soil compaction on harvesting extraction roads affect long-term productivity of Eucalyptus plantations in Zululand, South Africa? : scientific paperAuthor Colin W. SmithSource: Southern African Forestry Journal 2003, pp 41 –54 (2003)More Less
The effect of soil compaction on the growth of <I>Eucalyptus grandis</I> and two clonal hybrids (<I>Eucalyptus grandisx urophylla (E. gxu)</I> and <I>Eucalyptus grandis x camaldulensis (E. gxc))</I> was evaluated on harvesting extraction roads at three sites in the Zululand region of KwaZulu-Natal. Significantly lower initial survival was observed in the extraction road compared to the uncompacted area for <I>E. gxu</I> and <I>E. grandis</I>, the effect being site dependent whereas no significant differences were observed for <I>E. gxc</I> at any site. Soil compaction resulted in significantly lower tree growth on the extraction road at 8 years on a Constantia soil (4 to11% clay content) for all species/clonal hybrids (8 to 26% decrease) but there was no significant effect on tree growth at either of the other sites (8 and 5 year old stands) where the soils had a coarser texture. Even when a significant growth effect was observed in the extraction road the net effect on the compartment was reduced with increasing width between the extraction roads. Thus a 26% growth loss on an extraction road corresponded to a 3, 7% decrease in volume in the compartment in a 7th row extraction system. The paper emphasises the difficulty in quantifying growth losses since growth varies in a cyclical manner with distance from the extraction road. The lack of substantial growth losses on old extraction roads is attributed to relatively low levels of soil strength even when compacted, increasing available water capacity with increasing bulk density on very sandy soils, non-critical aeration levels when compacted and the effects of old tree roots providing access through compacted zones. This work has shown that, provided controlled traffic is practised rotation after rotation, the effects of harvesting extraction roads on the productivity of <I>Eucalyptus</I> plantations on sandy soils in Zululand are not pronounced.
Source: Southern African Forestry Journal 2003, pp 55 –63 (2003)More Less
The black wattle breeding programme that has served the wattle bark industry of South Africa for the past five decades put little emphasis on improving the yield and quality of the timber, as timber was not the product of importance. Today the timber is as important, if not more so, than the bark. A decision was taken, by the industry to re-design the breeding and production strategy for the species in South Africa, to improve timber yield and quality while maintaining an acceptable bark quality. Using the available seed at the ICFR at present, a Multiple Population Breeding Strategy has been chosen. The sub-populations have been established using the origin of the seed as the determining factor. Five sub-populations were established in KwaZulu-Natal during November 2002. The sub-populations were designed as progeny tests and as seedling seed orchards planted adjacent to one another. The performance of the families in the progeny tests will determine the management of the seed orchards. Generation turnover will be via open pollination in the initial years. Once a nucleus population is established, controlled pollinations may be used. The benefits from this strategy will be passed on to the industry in the form of improved seed.
Potential for genetic improvement of yield of exotic softwood tree species in Rwandan plantation forestry : research noteSource: Southern African Forestry Journal 2003, pp 65 –75 (2003)More Less
Exotic softwood tree species play a major role in Rwandan plantation forestry. They are used to produce sawn timber used for various purposes. <I>Pinus patula</I> is the major commercial species. Growth and yield of this species were compared in terms of seed source variation based on two trials, one established in Muhanga- Ndiza, Mushubati District, Gitarama Province at 16 years and another in Cyeru District, Ruhengeri Province at 15 years. Yield comparison was also made between <I>P. patula</I> and other new species being tested namely <I>P. caribaea, P. kesiya, P. maximinoi</I> and <I>P. tecunumanii</I>. <br>Although results are variable, it seems that genetic gains are possible in <I>P. patula</I> through the use of appropriate geographic sources. Land races from other African countries may play a major role in establishing a simple breeding strategy based on more seed introductions. Very significant improvements in volume production can be achieved through the use of other promising species such as <I>P. maximinoi</I> and <I>P. tecunumanii</I>. Further testing and improvement may confirm the potential of the two species since the current conclusions were drawn from results from small trials. Further improvements may possibly be achieved by introducing other tropical pine species such as <I>P. oocarpa</I> and also through crossing of related species. Unlike the other pine species, <I>P. kesiya</I> proved to be poorly adapted to local conditions and should not be considered in Rwanda as a plantation tree species. It is recommended that improved germplasm from external sources be included to accelerate the tree improvement programme for the most promising species in Rwanda.
African sandalwood (Osyris lanceolata) : resource assessment and quality variation among populations in Tanzania : research noteSource: Southern African Forestry Journal 2003, pp 77 –88 (2003)More Less
African sandalwood (<I>Osyris lanceolata</I>) populations occurring in Tanzania were assessed to determine the current resource status and ascertain variation in quality existing among them. This will provide a guide in the selection of populations where conservation efforts and improvement programmes can be concentrated. The resource status was assessed through estimation of the species' density per unit area and measurements of tree dimensions. Quality variation was assessed by determining the amount of oil extracted from a given amount of wood and the proportion composition of santalol, a prime determinant of sandalwood oil quality. The study revealed that populations supporting <I>O. lanceolata</I> in Tanzania occur mostly in arid to semiarid areas with the majority being on stony and rocky soils. However, big sized trees are supported in humid climates, being favoured by relatively low soil pH and reasonable amounts of soil nitrogen. Tree density ranged from 38 individuals to 76 per hectare. The mean tree height was 3, 8 m (2, 1 to 6, 5 m) while the mean diameter was 5, 7 cm (3, 6 cm to 8, 6 cm). The best quality and quantity of oil came from populations of relatively arid climates compared to those of humid climates. Populations differed significantly in both yield and quality. The highest yield obtained was 8, 45 ± 0, 54% from Gubali population while the highest santalol content (32, 2 ± 1, 2%) was from Bereko populations. Within trees, quantity and quality of oil was higher in wood portions close to the ground in both the root and shoot system. The amount decreased toward the root and shoot tip. The root and the shoot system were similar in quality and quantity of oil. The observed harvesting selectivity is thus primarily influenced by quality differences among populations while the large dimension and density differences among populations seem to be secondary. Inclusion of the root systems during harvesting is also a matter of maximizing the raw material to be collected rather than differences between the two portions. The exact factors controlling wood quality in the species have however remained uncertain. Probably, genetic factors alone or in combination with the environmental factors play a significant role.